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  • Articles  (4)
  • Bulletin of the Seismological Society of America (BSSA)  (1)
  • Bulletin of the Seismological Society of America (BSSA) 101: 2737-2754.  (1)
  • Bulletin of the Seismological Society of America (BSSA). 2011; 101(6): 2737-2754. Published 2011 Dec 01. doi: 10.1785/0120110109.  (1)
  • Bulletin of the Seismological Society of America (BSSA). 2013; 103(2A): 759-772. Published 2013 Mar 21. doi: 10.1785/0120120248.  (1)
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  • Geosciences  (4)
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  • Articles  (4)
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  • 1
    Publication Date: 2011-12-01
    Description: The detectability of low magnitude seismic events in the European Arctic is determined primarily by the small-aperture International Monitoring System arrays ARCES and SPITS. In August 2004, the SPITS array was upgraded to a broadband array with an increase in the sampling rate from 40 to 80 Hz. Most important, however, for the detection and location of small-magnitude seismic events was the deployment of three-component instruments at six of the nine sites. Detection and correct classification of secondary phases are of paramount importance for events observed by only a small number of stations at regional distances; and, in the absence of the strong Lg phases typically observed for continental propagation paths, multiple three-component stations were deemed necessary to exploit the higher S-phase amplitudes anticipated on the horizontal sensors. We demonstrate improved signal-to-noise ratios (SNRs) for S phases on horizontal beams for several events close to Novaya Zemlya. Horizontal component f-k analysis improves direction estimates and phase classification for low-SNR signals. We demonstrate secondary phases that are misidentified by vertical-only f-k analysis but which are correctly classified by three-component array processing. A significant problem with array processing at SPITS is the overlap in slowness space of regional P and S phases. Phase identification is improved greatly by comparing the coherence between vertical traces with the coherence between horizontal traces. Considerations in the routine array processing of SPITS data are reviewed, including the need for elevation corrections in slowness estimation and the need to take into account azimuth-dependent variation of apparent velocity estimates for regional phases.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Location Call Number Expected Availability
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  • 2
    Publication Date: 2013-03-22
    Description: We have investigated the Reviewed Event Bulletin (REB) of the International Data Center (IDC) for the time period 1 January 2001 to 31 December 2011 in order to quantify the event detection capability of individual seismic stations of the International Monitoring System (IMS). In order to obtain regionalized detection thresholds, we divide the events into a binned global grid system and investigate three estimation algorithms applied to each specific target area. Our preferred algorithm is to consider the ensemble of REB reported events in the area, and downscale each event magnitude with the observed signal-to-noise ratio (SNR) at the station. In this process, it is necessary to take into account events not detected by the station, in order to avoid a bias in the threshold estimate. We address this problem by using a maximum-likelihood estimation procedure whenever information on nondetections is available in the REB and correct for an estimated bias in other cases. A major result of this study is quantification and ranking of the IMS primary and auxiliary seismic stations based on their capability to detect events within regional and teleseismic distance ranges. We note that for each station, source regions with noticeable signal amplitude focusing effects (bright spots) and defocusing effects can be identified and quantified. We apply the results of this study to calculate updated global detection capability maps for the IMS primary seismic network.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Location Call Number Expected Availability
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  • 3
    Publication Date: 2013-03-21
    Description: We have investigated the Reviewed Event Bulletin (REB) of the International Data Center (IDC) for the time period 1 January 2001 to 31 December 2011 in order to quantify the event detection capability of individual seismic stations of the International Monitoring System (IMS). In order to obtain regionalized detection thresholds, we divide the events into a binned global grid system and investigate three estimation algorithms applied to each specific target area. Our preferred algorithm is to consider the ensemble of REB reported events in the area, and downscale each event magnitude with the observed signal-to-noise ratio (SNR) at the station. In this process, it is necessary to take into account events not detected by the station, in order to avoid a bias in the threshold estimate. We address this problem by using a maximum-likelihood estimation procedure whenever information on nondetections is available in the REB and correct for an estimated bias in other cases. A major result of this study is quantification and ranking of the IMS primary and auxiliary seismic stations based on their capability to detect events within regional and teleseismic distance ranges. We note that for each station, source regions with noticeable signal amplitude focusing effects (bright spots) and defocusing effects can be identified and quantified. We apply the results of this study to calculate updated global detection capability maps for the IMS primary seismic network.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2011-12-01
    Description: The detectability of low magnitude seismic events in the European Arctic is determined primarily by the small-aperture International Monitoring System arrays ARCES and SPITS. In August 2004, the SPITS array was upgraded to a broadband array with an increase in the sampling rate from 40 to 80 Hz. Most important, however, for the detection and location of small-magnitude seismic events was the deployment of three-component instruments at six of the nine sites. Detection and correct classification of secondary phases are of paramount importance for events observed by only a small number of stations at regional distances; and, in the absence of the strong Lg phases typically observed for continental propagation paths, multiple three-component stations were deemed necessary to exploit the higher S-phase amplitudes anticipated on the horizontal sensors. We demonstrate improved signal-to-noise ratios (SNRs) for S phases on horizontal beams for several events close to Novaya Zemlya. Horizontal component f-k analysis improves direction estimates and phase classification for low-SNR signals. We demonstrate secondary phases that are misidentified by vertical-only f-k analysis but which are correctly classified by three-component array processing. A significant problem with array processing at SPITS is the overlap in slowness space of regional P and S phases. Phase identification is improved greatly by comparing the coherence between vertical traces with the coherence between horizontal traces. Considerations in the routine array processing of SPITS data are reviewed, including the need for elevation corrections in slowness estimation and the need to take into account azimuth-dependent variation of apparent velocity estimates for regional phases.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
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